The objective of this project is to re-engineer a murine monoclonal antibody (MAb) by recombinant DNA technologies in order to more effectively treat breast carcinoma patients by the in vivo administration of radioimmunoconjugates. Phase I is focused on the generation of a "humanized" MAb (MA5), which reacts with a mucin - like, breast tumor- associated antigen. Reverse transcribed RNA from the MA5-expressing murine hybridoma will be amplified by the polymerase chain reaction (PCR) using Ig variable heavy and light chain-specific primers, and cloning and sequencing. Selection of the human framework regions (FRs) will then be based on sequence similarities to the mouse FRs, and the mouse complementarity-determining regions (CDRs) and their supporting human FRs will be modeled. Synthesis of the variable domains will proceed by PCR amplification of long, overlapping synthetic DNA oligomers encoding the designed sequences and these constructs are completed by ligation into expression vectors bearing human heavy (IgG1) and light chain (k) constant domains. After transfection, antibody expression will be monitored and compared to the holomurine MAb with regard to antigen recognition/binding. Phase II studies will compare the humanized and murine MAbs for targeting tumors in breast cancer patients.